1. Field of the Invention
The present invention relates to a film forming method and, more particularly, a method of patterning a film by using resist patterns, which are formed via exposure and development, as a mask after the resist has been coated on the film.
2. Description of the Prior Art
The step of patterning a film by using the photolithography technology is included in manufacturing the semiconductor device. In the photolithography technology, resist patterns which are formed by exposing and developing resist being coated on the film are employed as a mask. In exposure of the resist, a latent image is formed by transferring light shielding patterns formed on a reticle onto the resist.
Normally the light shielding patterns of the reticle are formed of chromium or chromium oxide, and they are formed via following steps by using the photolithography technology.
First, as shown in FIG. 1A, a light shielding film 102 formed of chromium or chromium oxide is formed of a quartz substrate 101, and then a radiation-induced polymerization type resist 103 is coated on the light shielding film 102 as photosensitive material and then prebaked.
Then, as shown in FIG. 1B, the latent image is depicted on the resist 103 by electron beams, for example. Then, as shown in FIG. 1C, patterns are formed by developing the latent image on the resist 103 by the developing process.
Then, as shown in FIG. 1D, the patterns of the resist 103 are transferred onto the light shielding film 102 by etching portions of the light shielding film 102 being exposed from the patterns of the resist 103.
Finally, as shown in FIG. 1E, the resist 103 is removed from the quartz substrate 101 by exposing the resist 103 to oxygen plasma or immersing the resist 103 in a mixed solution of sulfuric acid and hydrogen peroxide solution.
With the above, formation of the reticle has been terminated. In this case, if material having a gelling action, e.g., polystyrene is employed as the resist 103, developed residues are easily caused. The developed residue corresponds to such a phenomenon that the resist remains on unnecessary locations because of incomplete development of the resist.
If such developed residues are caused, there have been problems described in the following. First, linearity of edges of the patterns of the light shielding film 102 is deteriorated. Second, side portions of the patterns of the light shielding film 102 are formed like a taper to thus reduce the pattern precision. Third, the film below the resist 103 is etched incompletely because the resist 103 remains thin like islands on regions from which the resist 103 is to be essentially removed. Such unnecessary island-like resists are called "developed residues of resist" hereinafter.
These problems are now being overcome by the process which is called the "descum" step.
The descum step is defined as a step of removing the developed residue of resist by etching slightly the resist by using the oxygen plasma after exposure and development of the resist have been finished, or a step of removing the developed residue of resist by means of oxidation irradiated by the ultraviolet rays (UV) onto the resist in the oxygen containing atmosphere after exposure and development of the resist have been completed.
To irradiate the ultraviolet rays onto the developed residue of resist in such oxygen containing atmosphere is set forth in Patent Application Publication (KOKAI) Sho 58-218126. The ultraviolet ray irradiation is carried out in the vacuum evaporation equipment.
To employ the deep ultraviolet rays (DUV) in place of the ultraviolet rays is set forth in Patent Application Publication (KOKAI) Sho 61-77852, Patent Application Publication (KOKAI) Hei 4-302427, Patent Application Publication (KOKAI) Hei 3-154330, Patent Application Publication (KOKAI) Sho 61-108135, and Patent Application Publication (KOKAI) Sho 57-66633.
As the oxygen containing gas, the air is employed in Patent Application Publication (KOKAI) Sho 61-77852, the ozone is employed in Patent Application Publication (KOKAI) Hei 4-302427, and the oxygen is employed in Patent Application Publication (KOKAI) Sho 57-66633, Patent Application Publication (KOKAI) Sho 61-108135, and Patent Application Publication (KOKAI) Hei 3-154330.
However, it needs a large-scaled and high-priced plasma generating equipment to employ the oxygen plasma as the descum step.
Also, it does not need particularly the large-scaled equipment to employ the ultraviolet ray irradiation and the oxygen atmosphere as the descum step. Nevertheless, such descum step cannot remove the unnecessary resist in a short time, so that throughput cannot be improved.
In addition, if such descum process is continued until the unnecessary resist has completely been removed, the shape of the resist patterns acting as a mask is damaged.